1. Technical Field
The present invention relates to a profile creation method, a profile creation program, and a printing apparatus.
2. Related Art
A color conversion profile is information representing a correspondence relationship between an input color system and an output color system, which is used in the form of a color conversion look-up table, a color conversion function, or the like. A coordinate value of an input color system in a color conversion look-up table indicates a position of a point in a color space of the input color system, and a coordinate value of an output color system indicates a position of a point in a color space of the output color system. In this specification, a point in an arbitrary color space will also be referred to as a “color point” or a “lattice point”. In addition, color point represented by an input value and a color point represented by an output value registered in the color conversion look-up table will also be referred to as an “input lattice point” and an “output lattice point”, respectively.
As a technique for smoothing an arrangement of input lattice points and output lattice points in the color conversion look-up table, a technique described in JP-A-2006-197080 which has been disclosed by the present applicant can be exemplified. According to such smoothing, an optimal ink amount for reproducing L*a*b* lattice points after movement is determined by optimization processing with the use of an object function after the movement of the lattice point in a Lab color system. The optimal ink amount is determined as an ink amount for minimizing the object function.
However, since a color forming feature (hue value feature) with respect to the same ink amount is different for each kind of printing medium, and an ink amount (duty limit value) which can adhere to a unit area is also different, there is a problem in that it is necessary to prepare an object function for each kind of printing medium in order to create a color conversion look-up table for a plurality of printing media.
Moreover, since an object function includes a term for evaluating an image quality based on a hue value of a color reproduced when each amount of ink adheres to a printing medium, there is a problem in that it is necessary to prepare a color prediction model, which is for predicting a hue value based on an ink amount, for each kind of printing medium. Preparation of a color prediction model and the like for every kind of printing media requires great effort and resources. Therefore, it can be considered that color prediction models for some kinds of printing media (basic media) are prepared in advance and hue value prediction based on an ink amount is performed with the use of the color prediction models prepared for the basic media when a color conversion look-up table is created for every kind of printing media (diverting media) for which color prediction models have not been prepared. That is, prediction of a hue value based on an ink amount is executed with the use of the color prediction models prepared for the basic media, an ink amount is optimized by an object function based on the predicted hue value, and a color conversion look-up table for diverting media is created based on the ink amount determined through the optimization.
However, a color forming feature with respect to an ink amount is different for each printing medium as described above. Therefore, there is a concern in that in a color conversion look-up table for diverting media, which is finally obtained by executing hue value prediction with the use of the color prediction models prepared for the basic media and optimization of the ink amount by the object function, a defined ink amount (output lattice points) is eccentrically located in a certain color region (for example, an ink amount which realizes a relatively dark color formation is prescribed as many output lattice points on the diverting media), for example. Such eccentric location of the lattice points in the color conversion look-up table adversely affects later color management or further profile creation with the use of the color conversion look-up table.